file filename...
file displays the type of file filename..., in a two-column format: the first column represents the file name, and the second represents the file type (examples are ascii, data, C-shell commands, PostScript document, directory, commands, text, assembler, etc.)
prompt> file course.tex course.ps
course.tex: ascii text
course.ps: PostScript document
If the parameter to file is core, file will return the name of the executable file which caused the core file to be created.